Ohio Rev. Code Ann. § 153.28

When approved by the building commission, the plans, drawings, representations, bills of material, specifications of work, and estimates of cost thereof shall be filed by the county auditor in his office and shall not be altered, unless such alteration is first drawn, specified, and estimated as required by law for the original plans and approved by the commission. No such change shall be made until the price to be paid therefor has been agreed upon in writing between the commission and the contractor.